Simian sarcoma virus (SSV) is the only known transforming retrovirus of primate origin. The nucleotide sequence analysis of the cloned tranforming gene of SSV revealed a 675 nucleotide long open reading frame with a coding capacity for a protein of around 27,000 molecular weight, commencing 19 bases in the helper viral sequences. Thus the helper virus provided the regulatory elements for the expression of transforming gene. Based on data obtained from sequence analysis, antibodies were developed against a synthetic peptide of the predicted SSV transforming protein. These antibodies specifically precipitated a protein of about 28,000 MW in cells transformed by SSV, indicating it to be the product of the SSV transforming gene. The nucleotide sequence of the long terminal repeat (LTR) of SSV revealed functional regulatory elements like promoter, mRNA capping site and polyadenylation signal. A comparison of the SSV LTR sequence with LTRs of other type C retroviruses demonstrated that functionally important domains of LTRs have been conserved during evolution.